Answer
An icon column needs to be explicitly mapped to its own conditional-formatting rule — under the Formatting section in Element Designer, select the icon column in the Mapped Column dropdown, then define the conditions that determine which icon/color is shown (for example, a green circle when a State column equals 'Released', and a red X otherwise). Copying an existing element's icon column without also copying or recreating that formatting mapping leaves the icon column referencing formatting rules that don't actually exist for the new element, which is what causes this null-reference error specifically in Aurena. The same Mapped-Column-plus-conditions approach can be used to conditionally format other column types too, not just icons.